| Returns `true` if the pointer is null. |
| |
| Note that unsized types have many possible null pointers, as only the |
| raw data pointer is considered, not their length, vtable, etc. |
| Therefore, two pointers that are null may still not compare equal to |
| each other. |
| |
| # Panics during const evaluation |
| |
| If this method is used during const evaluation, and `self` is a pointer |
| that is offset beyond the bounds of the memory it initially pointed to, |
| then there might not be enough information to determine whether the |
| pointer is null. This is because the absolute address in memory is not |
| known at compile time. If the nullness of the pointer cannot be |
| determined, this method will panic. |
| |
| In-bounds pointers are never null, so the method will never panic for |
| such pointers. |
